Electronic computer circuits



Dec. 27, 1960 H. SCHMID ELECTRONIC COMPUTER CIRCUITS Filed June 19, 1959 INVENTOR MW ATTORN EY ELECTRONIC COMIUTER CIRCUITS Hermann Schmid, Binghamton, N.Y., assignor to General Precision, Inc., a corporation of Delaware Filed June 19, 1959, Ser. No. 821,520

Claims. (Cl. 235-196) This invention relates to electronic computing circuits, and more specifically, to an improved all-electronic, fourquadrant, analog divider circuit. In the analog computer, automatic control and instrumentation arts, it is frequently necessary or desirable to provide apparatus which will receive input signal variables commensurate with a dividend and a divisor, and which will provide an output signal commensurate with a quotient. The mathemetical operation of division differs from the operations of addition, subtraction, multiplication and integration in that the output, or answer, goes to infinity if one of the input variables, the divisor, becomes zero. One common prior art division technique involves the use of a feedback multiplier, wherein the [3, the feedback proportionality factor, is controlled in accordance with the divisor. In such circuits, the divisor may not be varied through both plus and minus values, since positive feedback will cause the feedback multiplier to oscillate. A related limitation exists in prior art servo division circuits, so that the servo runs to a limit stop if the divisor becomes zero.

A division circuit in which the dividend may be of either polarity, but in which the divisor must be of one polarity only is known as a two-quadrant divider. A division circuit in which both the dividend and the divisor may be of either polarity is known as a fourquadrant divider. To operate properly as a four-quadrant divider, it is necessary that the sign, or polarity, of the output signal always be properly related to the polarities of the dividend and divisor input voltages. It is a primary object of the present invention to provide an improved divider of the latter type, which is all-electronic, i.e., that has no mechanically moving parts, and which is simple, economical and reliable.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which the single figure is an electrical schematic diagram of an exemplary embodiment of the invention.

The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts, which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.

The present invention is in some respects a modification of and an extension of some basic principles and techniques disclosed in my copending applications Serial No. 693,298, filed October 30, 1957, and Serial No. 761,200, filed September 15, 1958, of which the present invention is a continuation-in-part, and to which reference may be had.

In the exemplary embodiment of the invention shown inv the drawing, the dividend variable input voltage V is applied at terminal 10 and the divisor variable input voltage V, is applied at terminal 11. As indicated by the 2,966,367 Patented Dec. 27, 1960 plus and minus signs on the drawing, either of these input voltages may be either positive or negative with respect to ground reference potential. If the V voltage is proportional to a variable x, and if the V voltage is proportional to a variable y, the output voltage V at terrnnial 12 will be proportional to x/y, the quotient of x and y.

The V input voltage is applied via scaling resistor R-l to the input circuit of direct-coupled amplifier U-101, which may be of conventional type. Also applied to the input circuit of U-101 via scaling resistor R-2 is a degenerative feedback voltage, which is compared with the V voltage for deriving an error potential to actuate amplifier U-101. The output voltage from amplifier U-101 is superimposed upon a periodic alternating modulating potential, such as a 1000 c.p.s. sine wave or saw-tooth wave potential, by means shown as comprising transformer T-ltil. An alternating potential is applied at terminals 13 and 14 to excite the primary winding 15. The DC. level of the secondary winding 16 of transformer T-101 is determined by the output voltage from direct-coupled amplifier U401, so that the composite potential applied to squaring amplifier U-102 consists of the superimposed potentials. Various other ways of superimposing two such potentials are well-known in the art and may be substituted. Squaring amplifier U-lii2 may take a variety of known forms. This amplifier is designed with high gain and overdriven, so that it saturates whenever its input signal exceeds more than 10 or 20 millivolts with respect to ground, thereby providing output potentials of substantially rectangular waveform. Exemplary suitable squaring amplifiers are shown in detail in my abovementioned copending applications. Squaring amplifier U-102 is designed to provide push-pull output potentials on conductors 18 and 20. These potentials are made to exceed the highest value of y voltage to be applied to terminal 11.

If the output conductor 17 of amplifier U-101 lies at ground potential, it will be apparent that the input potential to squaring amplifier U-102 will consist of two half-cycles of opposite polarity and equal time duration when a sine wave potential is applied to transformer T-101, thereby providing output potentials on conductors 18 and 20 which consist of positive and negative rec'- tangular pulses of equal time duration. If conductor 17 is positive with respect to ground, however, the input potential to amplifier U-102 during one cycle of the alternating potential will be seen to become positive with respect to ground for a period greater than one half-cycle and negative with respect to ground for a period less than one half-cycle, thereby providing an output potential on conductor 18 which consists of a positive rectangular pulse having a time duration greater than one half-cycle and negative rectangular pulse having a time duration less than one half-cycle, and further providing an inversely related set of pulses on conductor 20, where the time duration of the negative excursion exceeds the time duration of the positive excursion.

As shown in the drawing the rectangular pulses are applied to the collector electrodes of transistors T-l and T-2, which form a complementary transistor switching circuit, transistor T-Il being an NPN type and transistor T.-2 being a PNP type. plied via conductor 21 and resistors R 2 and R-3 to the base electrodes of transistors T-l and T-2. The control potential is derived by means of an electronic control circuit shown as comprising direct-coupled amplifier U-163 and oppositely-poled zener diodes X-l and X-2 connected as a feedback limiter. The y variable divisor voltage V is applied from terminal 11 via a scaling resistor R-4 to the input circuit of amplifier U403, which is provided with high gain. Whenever A control potential is ap-" the V voltage becomes more than one or two millivolts negative, a positive voltage of 22 volts, the Zener breakdown voltage of the two diodes, will appear on conductor 21. Conversely, whenever the V voltage swings more than one or two millivolts positive, a negative voltage of 22 volts will appear on conductor 21. It is in no way essential that the control voltage on conductor 21 be exactly and precisely the same for both polarities of V input voltages. The purpose of the Zener diodes is merely to limit the magnitude of the control voltage to prevent damage to transistors T-1 and T when the magnitude of V becomes great, since amplifier U103 is provided with high gain, and to prevent saturation of amplifier U-103, to avoid unnecessary delays in amplifier recovery which otherwise might result.

l"he polarity of the control voltage on conductor 21 determines which of the collector voltages of T-l and T-2 will appear at the common emitter terminal 23 of the transistor switch. For example, if the control voltage drives the transistor bases positive, the rectangular pulses on conductor 18 and the collector electrode of NPN transistor T-1 will appear at terminal 23, and conversely, if the control voltage is negative, the rectangular pulses on conductor 29 and the collector electrode of PNP transistor T-2 will appear at terminal 23. Thus it will be seen that amplifier U-103 comprises means for sensing the polarity of the divisor voltage and for controlling the operation of transistor switch 29.

The rectangular pulses at terminal 23 are applied to drive the base electrodes of an identical complementary transistor switch shown at 3% as comprising PNP transistor T-3 and NPN transistor T4, the collectors of which are excited by opposite polarity voltages cornmensurate in magnitude with the y variable, and the emitters of which are interconnected at conductor 24. The function of the complementary switch comprising transistors T-S and T-4 is that of a limiter and it operates to limit the amplitude excursions of the rectangular pulses from terminal 23 to magnitudes commensurate with the magnitude of the y variable voltage, V The amplitude-limited pulses at the common emitter terminal 24 are filtered by a conventional pulse-averaging or integrating filter 25 to provide the abovementioned degenerative feedback potential, providing a closed loop circuit. The closed loop circuit is provided with high gain, which causes the time widths of the rectangular pulses on conductors 18 and 20 to vary quite linearly with changes in the x variable input voltage, V regardless of whether the periodic alternating potential used is sinusoidal or sawtooth in character. Inasmuch as the 3: variable voltage V is applied to determine the magnitude of the degenerative feedback potential, variation in the V potential has an inverse effect from the effect of variation in the x variable voltage, V and thus the time widths of the rectangular pulses at terminal 23 vary in accordance with V /V or x/ y. A detailed mathematical treatment of the operation of a similar loop circuit is contained in my copending application, Serial No. 693,298 and need not be repeated herein. If desired, filter 25 may be replaced by a feedback capacitor (not shown) connected from output to input of amplifier U-101.

If the divisor or y variable voltage V were assumed always to be of a given polarity, either transistor T-l (or transistor I-2) would permanently connect the pulses from conductor 18 (or those from conductor 20) to terminal 23, and two-quadrant division, would be per:

formed by circuitry substantially identical to that of my copending application, Serial No. 693,298. The insertion of the switching circuit of T-l and T-2 in the loop, and control of this switching circuit in accordance with the sense of the y variable voltage V by the control voltage on conductor 21, serve to allow accurate and stable four-quadrant operation. Division through the two quadrants in which the divisor input voltage V is positive is effected by driving the bases of T4. and T-2 negative, thereby causing PNP transistor T-2 to connect the rectangular pulses present on its collector to terminal 23. Conversely, division through the two quadrants in which the V divisor voltage is negative is efiected by driving the bases of T-1 and T-2 positive, thereby causing NPN transistor T-1 to connect the rectangular pulses present on its collector to terminal 23. It should be noted that a change in the sense of the V, voltage at. terminal 11 also changes the respective polarities of the two opposite-polarity V voltages applied to the collectors of transistors T-3 and T-4. While this pair of opposite polarity voltages commensurate in magnitude with the y variable is shown in the drawing as being derived by the use of polarity-inverting feedback amplifiers, in many applications of the invention such input voltages may be provided by other means, such as, for example, oppositely-excited potentiometers on a y variable servo shaft.

The rectangular pulses at terminal 23 may be applied to drive the base electrodes of a further complementary switch 28 shown in block form which also functions as an electronic limiter. Switch 28 may be identical to switches 29 and 3t). Opposite-polarity voltages commensurate with a constant c or a further variable z are applied to the collector electrodes of switch 28, and the amplitude of the pulses appearing on conductor 31 will then be limited in accordance with either the constant c or variable z. The pulses on conductor 31 may then be applied to conventional pulse-averaging means such as filter 32 (shown in block form), to provide an analog output potential V at terminal 12 commensurate with If the x variable input potential changes in polarity, the output potential will similarly change in polarity inasmuch as the push-pull signals applied to switch 29 will reverse in polarity. If the y variable input voltage changes polarity, the output potential will similarly change in polarity because the control potential on conductor 21 will cause switch 29 to apply the other of the push-pull signals to terminal 23 and switch 28. However, if both the x variable input voltage and the y variable input voltage change in polarity, the same polarity push-pull signal will be continued to be applied to terminal 23 and switch 28. Thus it will be seen that the polarity of the output potential is correctly related to the signs of the dividend and divisor inputs throughout all four quadrants.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above descriptive or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense. Circuit values which are merely exemplary are shown in the drawing.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. An analog computer dividing circuit capable of four-quadrant operation, comprising in combination, timemodulation means responsive to an applied input dividend voltage and a feedback voltage for deriving first and second square-wave voltages on respective first and second conductors, said first voltage having a positive duration ratio which is commensurate with the value of a dividend input voltage and said second voltage having a negative duration-to-positive duration ratio which is commensurate with the value of said dividend input voltage; a complementary transistor switching circuit comprising two transistors of opposite conductivity types, each of said transistors having a base, an emitter and a collector electrode, said first and second square wave voltages being connected individually to the collector electrodes of said transistors and said emitter electrodes of said transistors being interconnected at a first terminal; means connected to an input divisor voltage for sensing the polarity of said divisor voltage and for providing a control voltage which varies in polarity when said divisor voltage varies in polarity, said control voltage being connected to the base electrodes of said transistors; a second transistor switching circuit comprising third and fourth transistors of opposite conductivity types each having a base, an emitter and a collector electrode; means for applying opposite-polarity potentials equal in magnitude to said divisor voltage to the collector electrodes of said third and fourth transistors, said first terminal being connected to the base electrodes of said third and fourth transistors and said emitter electrodes of said third and fourth transistors being interconnected at a second terminal; and circuit means including pulse-averaging means connected to said second terminal to apply said feedback voltage to said time-modulation means.

2. An electronic division circuit capable of four-quadrant operation, comprising in combination; first amplifier means responsive to a dividend input potential and a degerenative feedback potential for providing an error potential; means for superimposing a periodic alternating modulating potential on said error potential to provide a composite potential; second means for amplifying said composite potential to provide a pair of push-pull square wave potentials, a first transistor switch connected to apply one or the other of said square wave potentials to a second transistor switch and to a first terminal depending upon the instantaneous polarity of a divisor input potential, said second transistor switch being operable to limit the amplitudes of its applied square wave potentials in accordance with the magnitude of said divisor input potential to provide said feedback potential, circuit means for applying said feedback potential to said first amplifier means; means for sensing the polarity of said divisor input potential and providing a control potential, said control potential being connected to operate said first transistor switch; and pulseaveraging means connected to receive the potential at said first terminal, thereby to provide an output potential commensurate with the quotient of said divisor and dividend potentials.

3. Apparatus according to claim 2 having a third transistor switch connected between said first terminal and said pulse-averaging means, said third transistor switch being operable to limit the amplitude of square wave pulses applied to said pulse-averaging means in accordance with the value of a third independent variable.

4. Apparatus according to claim 2 in which each of said transistor switches comprises two opposite-conductivity types of transistors having a common emitter terminal.

5. An electronic dividing circuit capable of four-quadrant operation with correct polarity of output quotient signal, comprising in combination; a closed loop feedback circuit including an amplifier and time-modulation means responsive to an input dividend potential and a feedback potential for producing a pair of push-pull square wave potentials having time widths directly proportional to said dividend potential; electronic switching means responsive to a control voltage for selecting and applying one of said square wave potentials to first and second electronic limiter circuits, said first electronic limiter circuit being connected in said loop circuit and responsive to a first pair of mutually opposite-polarity input divisor potentials each of which vary in magnitude and polarity in accordance with a divisor variable for limiting said selected one of said push-pull square wave potentials to provide further square wave pulses; pulse-averaging means associated with said loop feedback circuit to integrate said further square wave pulses thereby to provide said feedback potential; said second electronic limiter circuit being controlled by a second pair of mutually opposite-polarity voltages commensurate in magnitude and sign with a further quantity and operative to limit said selected one of said push-pull square wave potentials in accordance with said further quantity to provide second further square wave potentials, second pulse-averaging means connected to integrate said second further square wave potentials to provide said output quotient signal; and means responsive to the polarity of one of said input divisor potentials for providing said control voltage to control said electronic switching means.

6. A circuit according to claim 5 in which said elec- IIOILlC switching means comprises first and second transistors of opposite conductivity types each having a base, an emitter and a collector electrode; each of said pushpull square wave potentials being connected individually to one of said collector electrodes, said control voltage being connected to each of the base electrodes of said transistors, and said emitter electrodes being interconnected to connect said selected one of said push-pull square wave potentials to said limiter circuits.

7. Apparatus according to claim 5 in which said means for providing said control voltage comprises a second amplifier responsive to one of said divisor potentials, and a pair of oppositely-poled zener diodes connected in series between the output circuit and input circuit of said second amplifier, thereby to provide a control voltage at the out put of said second amplifier which varies in polarity in accordance with variation in polarity of said one of said divisor potentials.

8. Apparatus according to claim 5 in which said means responsive to the polarity of one of said input divisor potentials for providing said control voltage comprises a feedback limiter circuit responsive to said one of said input divisor potentials.

9. A circuit according to claim 5 in which said first electronic limiter circuit comprises first and second transistors of opposite conductivity types each having a base, an emitter and a collector electrode; each of said divisor input potentials being connected to one of said collector electrodes, said selected one of said push-pull square wave potentials being connected to the base electrodes of said transistors, said emitter electrodes being connected to gether.

10. A circuit according to claim 5 in which said second electronic limiter circuit comprises first and second transistors of opposite conductivity types each having a base, an emitter and a collector electrode; each of said voltages of said second pair being connected to one of said collector electrodes, said selected one of said push-pull square waves being connected to said base electrodes, and said emitter electrodes being connected together.

No references cited. 

